According to intelligent transportation systems (ITS), many ongoing efforts are made to research and develop methods for exchanging various informations such as real-time traffic information and/or safety warning between vehicles. For example, ongoing efforts are made to research and develop vehicle communications for a proximity service (ProSe) and a public warning system. A communication interface for a vehicle can be commonly called V2X (vehicle-to-x). V2X communication may be categorized into V2V (vehicle-to-vehicle) communication, V2P (vehicle-to-pedestrian) communication, and V2I (vehicle-to-infrastructure entity) communication. V2V communication may refer to communication between vehicles. V2P communication may refer to communication between a vehicle and a personally carried device (e.g., a handheld terminal of a pedestrian or a bicycle rider). And, V2I communication may refer to communication between a vehicle and a roadside unit (RSU). RSU may refer to a traffic infrastructure entity. For example, RSU may include an entity that transmits a speed notification. For V2X communication, a vehicle, an RSU and a handheld device may be equipped with a transceiver.
As describe above, V2X communication may be used to indicate warnings for various events such as safety and the like. For example, information on an event occurring on a vehicle or road may be notified to another vehicle or pedestrians through V2X communication. For example, information on a warning of a traffic accident, a road situation change, or an accident danger may be forwarded to another vehicle or pedestrian. For example, a pedestrian, who is adjacent to or crossing a road, can be informed of information on vehicle approach. For example, information on such an event may be broadcasted to an ambient vehicle, pedestrian or RSU by a vehicle, pedestrian or RSU. Yet, another vehicle or pedestrian approaching a corresponding event occurring place may not be able to obtain the broadcasted information. Hence, the information on the event may be repeatedly broadcasted. Yet, in this case, due to the repeated broadcasting, resource overhead may increase as well as power consumption. Moreover, since a receiving end is unable to know when a broadcasting will occur, a communication device of a vehicle or pedestrian may be maintained in wake-up state. In this case, power consumption of the receiving end may increase. Hence, the demand for a V2X communication method capable of reducing power consumption as well as securing reception of information on an event is rising.
The present invention is devised to solve the above problems, and intends to propose a method of reducing power consumption as well as raising receptibility of information on an event through V2X communication. Particularly, the present invention proposes a method of informing other devices of an occurrence of an event using an alarm message besides a message containing actual information on the event.